Melanin-concentrating hormone (MCH) is a cyclic peptide that was first isolated from the pituitary of chum salmon (Kawauchi, Nature 305, 321-333). The sequence for MCH has been shown to be identical in all teleost fish where it causes melanin granulation and, hence, regulates color change. Recent reports also suggest MCH plays a role in food intake in teleosts. MCH also inhibits release of ACTH thus acting as an antagonist of α-MSH. MCH was subsequently identified in mammals as a cyclic nonapeptide. The first MCH receptor (later termed MCHR1) is a G-protein coupled receptor (GPCR) and was identified using a “reverse pharmacology” approach. That is, it was demonstrated that the natural ligand of orphan GPCR, SLC-1, was MCH in mammals. Subsequent to this determination, a second MCH receptor (MCHR-2) has been identified. The role of MCH in feeding behavior in mammals has been the subject of investigation for a number of years (Qu, et al. (1996) Nature, 380: 243-247; Rossi et al. (1997) Endocrinology 138: 351-355; Shimada et al. (1998) Nature 396: 670-674). MCH is predominantly expressed in the lateral hypothalamus and the zona incerta of the central nervous system (CNS). Central administration of MCH is known to stimulate food intake and regulate energy balance. MCH is upregulated in the lateral hypothalamus during fasting (Rossi et al. (1997) Endocrinology 138: 351-355). Knockout experiments have shown that mice lacking the MCH peptide are lean, hypophagic and maintained elevated metabolic rates. MCH mRNA levels are increased in both normal and obese mice. Transgenic mice that overexpress MCH are obese and insulin resistant. Genetically altered animals that lack the gene encoding the MCH receptor are moderately hyperphagic but show resistance to becoming obese and have an increased metabolic rate (Shimada et al. (1998) Nature 396: 670-674). MCH is thought to exert its effects on feeding behavior by binding to an MCH receptor (MCHR1 or MCHR2) resulting in mobilization of intracellular calcium and a concomitant reduction in cyclic AMP levels. The consistency in these findings suggests that MCH antagonism could safely lead to weight loss in humans. In further support of this, a number of studies describe statistically significant reduction of food intake in rodents following acute administration of MCH receptor antagonists and/or statistically significant reduction of body weight after chronic administration of small molecule MCH receptor antagonists (Borowsky et al. (2002) Nature Medicine 8(8):825-830; Souers et al. (2005) Bioorg. Med. Chem. Lett. 15: 2752-2757, Vasudevan et al. (2005) Bioorg. Med. Chem. Lett. 15: 4174-4179, Kym et al. (2005) J. Med. Chem. 5888-91; McBriar et al. (2005) J. Med. Chem. 48: 2274); Takekawa et al. (2002) Eur. J. Pharmacol. 438(3): 129-135; Kowalski et al. Eur. J. Pharmacol. (2004) 497: 41-47). The precise role of MCH in attenuating food intake is not clear from these studies because the small-molecule MCH receptor antagonists described are either 1) unselective for the MCH receptor or 2) no selectivity data is disclosed.
MCHR1 antagonism with a small molecule is now recognized as a promising strategy for the treatment of obesity. The following relate to small-molecule MCH receptor antagonists: Kato et al. WO2001/21577; Chen et al. WO2002/089729; Collins et al. WO2003/105850; Souers et al. US2005/0137243; Hulme et al. WO2005/019167; Tempest et al. WO2005/019240; Barvian et al. WO2004092181; Barvian et al. WO2005/042541; McKittrick et al. WO2002/051809; Sasikumar et al. WO2005/034947; Devita et al. WO2003/045313; Gillig et al. 2005/040257; and Schwink et al. WO2004/072025.
MCH has been shown to modulate behaviors and disease states other than hyperphagia and obesity. MCHR1 antagonists have been shown to inhibit behavior in rodents that models depression and anxiety in humans (Hervieu (2003) Expert Opinion on Therapeutic Targets 7(4), 495-511 and references therein; Georgescu et al. (2005) Journal of Neuroscience 25(11), 2933-2940; Chaki et al. (2005) Journal of Pharm. and Exptl. Therapeutics 313, 831-839). These rodent models include forced swim test, vocalization and various models of social interaction. Recent studies also support a role of MCHR1 in cognition (Adamantidis et al. (2005) European Journal of Neuroscience 21, 2837-2844).
There is still a need for selective MCH receptor antagonists in order to address the role of the MCH receptor in food intake and regulation of body weight. Unlike a number of existing medications for weight loss, it is believed that a selective MCH receptor antagonist would provide a means of safely reducing food intake and body weight in humans. Such selective MCH receptor antagonists would be useful for the treatment of, for example, obesity, hyperphagia, anxiety, depression and related disorders.